Traditionally, lies are detected using a polygraph lie detector. But lie detectors, which measure physiological responses, such as blood pressure and respiration, can be fooled because physiological responses can vary between individuals, and in some cases can be regulated, say the researchers.

Instead Faro and team tested 10 volunteers using functional magnetic resonance imaging or fMRI. The volunteers either lied or told the truth at the same time as their brains were scanned with a strong magnet.

In the study, six volunteers were asked to shoot a toy gun and then lie and say they didn't do it. Three others who watched told the truth about what happened. One volunteer dropped out of the study.

While giving their "testimony," the volunteers were hooked up both to a conventional polygraph and also had their brain activity imaged using fMRI, which provided a real-time picture of brain activity.

There were clear differences between the liars and the truth-tellers, said the researchers.

Faro said there might be unique areas in the brain involved in deception and truth-telling that can be measured with fMRI.

"We found a total of seven areas of activation in the deception [group]," he said. "We found four areas of activity in the truth-telling arm."

Overall, it seemed to take more brain effort to tell the lie than to tell the truth, the team found.

Lying caused activity in the frontal part of the brain including the medial inferior and pre-central areas, as well as the hippocampus and middle temporal regions and the limbic areas. Some of these are involved in emotional responses dealing with awareness, perception and inhibition, Faro said.

During a truthful response, the fMRI showed activation of parts of the brain's frontal lobe, temporal lobe and cingulate gyrus.

High tech lie detection

The study not only sheds light on what goes on when people lie but may also provide new technology for lie-detecting, the researchers said.

Although using fMRI as a lie detector is expensive, it may be worthwhile in some cases such as trying to question a terrorism suspect, or in a high-profile corporate crime case, Faro said.

Faro admitted the study was small and limited. Volunteers were not asked to try especially hard to deceive the equipment, he said.

He said it is too early to tell if fMRI can be "fooled" in the same manner, but added that his preliminary findings suggest a consistency in brain patterns that might be beyond conscious control.